Both computer software and digital audio recordings are commonly recorded on to compact discs (CDs). Computers, such as personal computers (PCs) read audio CDs differently than do consumer CD playback systems, such as car players, boom boxes, portable devices and hifi players, for example).
CDs are almost universally made in accordance with the following international standards:                International Standards Organization (ISO) 9660: Information Processing—Volume and File Structure of CD-ROM for Information Interchange, ISO Standard 13490-1        International Electrotechnique Commission (CEI-IEC) 908 (generally conforming to what is known as the “Red Book”)        ISO/IEC 10140 (generally conforming to what is known as the “Yellow Book”)        
Because the data recorded on compact disc is in a digital format with an error-correction capability, it is possible to make faithful copies whose playback is indistinguishable from that of the original disc from which the copy was made. Furthermore, equipment for producing compact discs is readily available and relatively inexpensive, both for stamped discs and for recorded discs. As a result, the unauthorized or illegal copying of compact discs has thus become a serious problem.
Consumers who have purchased inexpensive computer systems and CD recorders are capable of making copies of original CDs, thereby depriving the copyright owner of a sale.
Only suitable copy-protection methods can succeed in reducing the increasing flood of these unauthorized recorded disc copies. Unfortunately existing prior art copy-protection methods are unsuitable and/or inadequately effective for the audio compact disc.